1. Field of the Invention
The present invention relates to a deinking composition and a deinking method for use in the reclamation of waste paper including newspapers, magazines and waste office automation (OA) papers. More particularly, the present invention relates to a deinking composition and a deinking method whereby a deinked pulp can be obtained that has a high whiteness and a high b value with little contamination from unliberated ink spots, particularly unliberated large ink spots having a particle size of 30 .mu.m or more. The deinked pulp can be obtained from, for example, newspapers, magazines or waste OA papers by flotation, washing or a combination procedure thereof.
2. Description of the Related Art
It has been a practice to reclaim waste papers including newspapers, magazines and waste OA papers. Recently the effective utilization of waste papers has become more and more important in conjunction with the problems of the global environment such as the conservation of forest resources and refuse disposal. Further, it has been attempted to utilize deinked pulp as a pulp of a higher rank, for example, to reclaim old newspapers for use in making a paper of intermediate grade.
On the other hand, recent improvements in printing techniques, printing systems and printing ink compositions have made it difficult to deink waste papers. In order to facilitate deinking, therefore, attempts have been made to improve deinking devices.
Meanwhile, conventional deinking compositions are as follows. In order to remove inks and other impurities from waste paper, there have been used alkaline agents such as caustic soda, sodium silicate, sodium carbonate and sodium phosphate, bleaching agents such as hydrogen peroxide, hydrosulfites and hypochlorites, and sequestering agents such as EDTA and DTPA together with one or more deinking agents. The deinking agents include anionic surfactants such as alkylbenzenesulfonates, higher alcohol sulfates, .alpha.-olefinsulfonates and dialkyl sulfosuccinates, nonionic surfactants such as ethylene oxide adducts of higher alcohols, alkylphenols and fatty acids and alkanolamides. Although these deinking compositions show excellent foaming properties in the flotation step, their ability to collect ink are limited. In the washing step, on the other hand, they are poor in detergency and, furthermore, their good foaming properties cause trouble in the effluent disposal step. As a result, only a deinked pulp of a low grade can be obtained by these methods. In order to deink waste OA papers including plain paper copy (PPC) and computer print output (CPO), in particular, it is required to either apply a large shear force energy or use a large amount of alkalis, since printing inks (toners) used therein comprise styrene/acrylic binders or polyester binders, which differ from the conventional newspaper ink, result in large ink spots (i.e., a particle size of 30 .mu.m or more) remaining unliberated after the completion of a common deinking treatment. However, the use of a large amount of alkalis suffers from some disadvantages, including an increase in the sticky matters, the load in the effluent disposal step and the brittleness of the pulp. Thus no method for effectively deinking waste OA papers and blends thereof has been established so far.